Prosopis Juliflora the Invasive in Kenya Occurred in 1973 in Bamburi (Mombasa County), Near the City of Mombasa

The first documented case of Prosopis juliflora The invasive in Kenya occurred in 1973 in Bamburi (Mombasa County), near the city of Mombasa. species Prosopis In the years that followed, more individual plants were introduced until cultivation on a juliflora and its large and extensive scale began in 1983 in Baringo county and the Bura region (Taita- spread in coastal Taveta County). The large-scale cultivation of Prosopis juliflora was promoted by Kenya government agencies and NGOs, who recommended the plant due to its suitability for dry areas. It was not until 2008, when the Kenyan 1. Introduction minister for agriculture declared Prosopis juliflora a noxious weed (Maundu et al., 2009).

Biological invasions have become a major threat to global biodiversity. 2. Description Defined as the spread of invasive species, or alien species, biological invasion is one of the Prosopis juliflora is native to rangelands in main causes of species extinction. Mexico and Central and Northern South One example of such a biological invasion is America, where it grows as a shrub or small that of Prosopis juliflora (Sw.) DC, which is tree. Prosopis juliflora is colloquially known in considered a top global invasive species (de Kenya by its Swahili name, Mathenge, or, Souza Nascimento et al., 2014). more popularly, as Mesquite, which is a While there are many different definitions of general term used for many of the 44 species an invasive species, the most common one belonging to the genus Prosopis. All are part refers to an introduced species - indigenous to of the family Fabaceae, also called a different region - which grows quickly and Leguminosae (BioNET-EAFRINET, o. J.). vigorously, spreads over a wide geographic area and has a negative impact on biodiversity Prosopis juliflora can grow as a shrub or tree (Ehrenfeld, 2010). with a height of up to 15 m. It often has multiple stems, which tend to grow in a jagged In response to the growing threat posed by fashion. On each turn of the zig-zag shaped invasive species, the Convention on Biological branches, there are one or two thick thorns Diversity (CBD) was formed. The CBD, an that can reach up to 5 cm length. The bark is international environmental agreement signed grey-green in colour and becomes rougher by 168 countries, calls upon parties to and scalier with time. ‘prevent the introduction of, control or Bipinnate leaves, typical for Prosopis and eradicate those alien species which threaten other species of Fabaceae, are 6-8 cm long ecosystems, habitats or species’ (Article 8h). and made of 12-25 pairs of smaller pinnae. Since Prosopis juliflora is said to have a These narrow and tiny leaves usually range potential of invading nearly half of Kenya’s from 6-16 mm long and 1.5-3.2 mm wide. land area, rapid intervention is urgently The flowers of Prosopis juliflora are 5-10 cm required (Shackleton et al., 2014). long and look similar to a brush, composed of

dense yellow spikes. They turn into green 1 pods - of about 10-20 cm long, often slightly complete darkness and in a wide range of air curved – and become yellow when they ripen temperatures up to 50 °C and soil (BioNET-EAFRINET, o. J.). temperatures up to 70 °C (Damasceno et al., Inside each pod is approximately 10-20 small 2018). Although high soil salinity does have a oval seeds, that are dispersed by browsers negative impact on seed germination (El- such as goats, camels and some wild animals Keblawy & Al-Rawai, 2005), Prosopis juliflora is who feed on them. Seeds can also be generally capable of thriving in sandy, rocky, distributed by floodwaters and surface runoff poor and saline soils and reaches altitudes (Nawata, 2012). Overall, one tree can produce between 300-1900 m above sea level (BioNET- between 630,000 and 980,000 seeds per year EAFRINET, o. J.). Its rapid growth and large (de Souza Nascimento et al., 2014).The roots quantity of seeds also contribute to Prosopis of Prosopis juliflora reach deep into the juliflora’s survival and spread (Damasceno et ground to moist layers of soil and sub-surface al., 2018). water (El-Keblawy & Al-Rawai, 2005). In addition to characteristics that help survive Prosopis juliflora in very inhospitable regions, the species also benefits from defence mechanisms like thorns against herbivores and neighbouring plants. An additional adaptation that allows Prosopis juliflora to quickly invade and dominate an ecosystem is the ability to release allelochemicals from its roots, leaves and fruits. Allelochemicals are substances produced by organisms to react to abiotic and a. Thorns of Prosopis juliflora biotic factors in their environment. This in turn allows Prosopis juliflora to inhibit seed germination or growth of surrounding plants, while it is unaffected by other plants allelochemicals (Damasceno et al., 2018).

3. Use and problems

Use

The introduction of Prosopis juliflora to Kenya, as well as other countries in South and East Africa, many coastal regions of Asia and to b. Flowers of Prosopis juliflora America and Australia, occurred primarily in rural areas (de Souza Nascimento et al., 2014). Due to its origin, Prosopis juliflora is adapted People where told about the various to arid and semi-arid climates and so is advantages and economic benefits of Prosopis capable of surviving and growing in a harsh juliflora, such as using the plant for firewood desert environment. For example, the depth or charcoal production, shade and fodder for of the roots is an adaption to water scarcity. livestock. Seeds germinate in both full light and 2

Interviews with people of the Afar region in Problems Ethiopia on Prosopis juliflora revealed that the plant was frequently associated with animals By 2014, the Prosopis juliflora was found in and cattle (Wakie, Laituri, et al., 2016). 129 countries (Shackleton et al., 2014), where it was fought as an invasive species. Such Moreover, Prosopis juliflora was introduced to plants are defined as introduced species, prevent further soil degradation from capable of growing fast and spreading widely, advancing desertification that occurs in many hence having a negative impact on arid and semi-arid regions due to activities like biodiversity and ecosystems (Ehrenfeld, 2010). overgrazing and deforestation. As stated Todayc, Prosopis juliflora is considered above, Prosopis juliflora is capable of surviving internationally to be among the most in harsh environments and has the potential problematic invasive species (de Souza to stabilize sandy ground sensitive to erosion Nascimento et al., 2014). (Nawata, 2012). Additionally, as with many other leguminous plants, it is capable of While initially introduced as a desired plant, creating a symbiosis with Rhizobia, a group of governments, NGOs and scientists realized the bacteria that allows these plants to fix risks and dangers posed by Prosopis juliflora, it atmospheric nitrogen, which ultimately caused a change of perspective. For example, fertilizes the soil (de Souza Nascimento et al., after its introduction at the beginning of the th 2014). 20 century, the Sudanese government Due to these perceived benefits, the Ethiopian stopped planting Prosopis juliflora in the government even initiated a programme 1990s and started programs to eliminate it planting Prosopis juliflora in the 1970's to (Nawata, 2012). There are now numerous “green” the region of Gewane and Amibarato, studies as well as publications by government limit further desertification and prevent administrations describing the dangers posed drought (Wakie, Laituri, et al., 2016). by Prosopis juliflora and presenting various approaches to address its spread. Studies have also investigated the antifungal In comparison to many native species, and antibacterial activity and potential use of Prosopis juliflora has a higher competitive the plant (Damasceno et al., 2017). advantage. While indigenous plants of Furthermore, Prosopis juliflora’s wood is used rangelands may also be adapted to their as timber for the construction of furniture or environment, they lack the necessary defence fences (Wakie, Laituri, et al., 2016), and for mechanisms to compete with or restrict various medicinal purposes. For example, a Prosopis juliflora. This issue also applies also South African company has developed a to agricultural plants (de Souza Nascimento et medicine derived from Prosopis juliflora’s al., 2014). pods to lower people’s blood sugar. Other uses of Prosopis juliflora are in the cosmetic The allelochemicals released by Prosopis industry, biotechnology and even in the food juliflora inhibit the growth and seed industry, since it is possible to produce food germination of nearby plans, whereas items like flour from Prosopis juliflora Prosopis juliflora itself is immune to the (Damasceno et al., 2018). allelochemicals of other plants (Damasceno et al., 2018). Additionally, Prosopis juliflora grows much faster than many other plants and so reduces the available space by rapidly forming dense thickets. These adaptations 3 make it nearly impossible for nearby native substances in the pods. Toxicity occurs when plants to grow (Wakie, Laituri, et al., 2016). the pods are eaten almost exclusively and Hence, indigenous species are being pushed over a long period of time, which often occurs back by the spread of Prosopis juliflora, during droughts as the pods form an resulting in changes to regional ecosystems important part of the animal’s fodder during and causing shifts in spatial patterns (Nawata, this time. Ultimately, animals suffer from 2012). A decrease of individuals of indigenous muscle dysfunctions, weight loss and even species may also lead to a complete death (Damasceno et al., 2017; Nawata, extinction. When the direct cause of 2012). People also observed other extinction is identifiable, introduced species phenomena like diarrhoea, the loss of goats’ are the most common one (McNeely, 2001). teeth or fruit gum that sticks to them, fibrous remains blocking animals rumens (Chepkwony, 2018; Maundu et al., 2009) and also physical injuries from the thorns (Wakie, Laituri, et al., 2016).

While all types of animals are affected, cattle and camels are on top of the list, followed by sheep and goats. The death of livestock often comes along with a degradation of people’s livelihood (Wakie, Laituri, et al., 2016).

c. Thickets of Prosopis juliflora Yet, people are also affected directly by Prosopis juliflora, not only through their Due to the complex structure of ecosystems, a animals. The rapid growth of enormous change in the flora also causes a change in the thickets depletes water resources and fauna. Herbivore insects have adapted to prevents both people and animals from indigenous plants during evolution. With their reaching water wells or other infrastructures decrease the quality and quantity of food for (Shackleton et al., 2014; Wakie, Laituri, et al., insects may drop, both species-related and 2016). individual-related (Proche et al., 2008). Furthermore, thickets can be a hiding place for Particularly at risk are those species, that rely criminals and dangerous animals (Maundu et on just a few plants to feed on (oligophagous), al., 2009; Wakie, Laituri, et al., 2016). or even just one species (monophagous). The impact on insects can then further Moreover, the purported economic benefit of influence their predators, like, for example, Prosopis juliflora through charcoal sales is no birds. This ripple effect can continue until the longer applicable, as the Kenyan government whole ecosystem has changed. These instituted a moratorium on unlicensed logging consequences are difficult to understand and and charcoal production. predict. In terms of soils, Prosopis juliflora can stabilize Other ways that Prosopis juliflora affects local sand dunes and so prevent erosion. fauna is through its allelochemicals. Although Nevertheless, this isn’t applicable to all areas, Prosopis juliflora is used for animal feed, it can as in other cases it enhances the loss of fertile be harmful to them due to poisonous soil and growth of massive sand dunes (Nawata, 2012; Shackleton et al., 2014). 4

4. Spread in Kenya Wakie et al. (2016) notes that the native plants displaced by the invasive species are Today, Prosopis juliflora is invasive in many often the ones indigenous people rely on for countries away from its original distribution different uses like construction materials and areas in Mexico and North and Central South furniture, tools, firewood, food, medicinal America. In 2009 it had already spread purposes and most importantly animal food throughout the arid and semi-arid regions of (Wakie, Laituri, et al., 2016). Particularly North, West, East and Southern Africa, the affected are fodder plants like different grass West of the Arabian peninsula, South East species and Acacia trees (Maundu et al., 2009; Asia, South West Australia, Southern USA and Wakie, Laituri, et al., 2016). the South of Brazil and Uruguay (Maundu et The displacement of native plant species also al., 2009). In 2014, Prosopis juliflora was results in a dependence on Prosopis juliflora, documented in 129 countries (Shackleton et because it is widely available in their al., 2014). environment and there is a lack of alternatives to meet livelihood demands (Maundu et al., In Kenya, the rapid spread began in the 2009). regions of the first large-scale plantations – Further, one of the biggest dangers of Baringo County and Bura (Taita-Taveta Prosopis juliflora is the physical danger they County), but also in Turkana County, where pose. Not only do the thorns puncture and the densest thickets can be found today. damage shoes, tires and so on, they also hurt Generally, arid and semi-arid areas have the people. Maundu et al. (2009) investigated the largest infestations. In Kenya, this includes the spread and impact of Prosopis juliflora in East and North East the country as well as Kenya and interviewed people from different regions in the Rift Valley and on the coast. In regions. On top of the list of threats people drier areas, Prosopis juliflora benefits from named where physical injuries, that lakes (Lake Baringo), river systems (Tana and sometimes resulted not only in pain but also Turkwel) and seasonally flooded areas like the in infection or even death. Lotikipi plains and disturbed areas such as Prosopis juliflora is also connected to Malaria. farms and urban areas (Maundu et al., 2009). A study in Mali investigated the connection The rivers Turkwel and Tana - including Tana between the invasive species and various River Primate National Reserve and Arawale parameters of Anopheles mosquitos, which National Reserve - and the Lotikipi Plains are transmit the parasites Plasmodium particularly sensitive ecosystems, that are now responsible for Malaria. The results confirmed threatened by Prosopis juliflora. The plains that the existence of Prosopis juliflora form an important grazing area for the local enhanced the mosquito’s transmission Turkana people. Other conservation areas capacity of Plasmodium (Muller et al., 2017). affected include the Lake Bogoria National

Reserve, Shaba National Reserve, Samburu This finding further demonstrates the need to National Reserve and Marsabit National take action and to join other countries already Reserve as well as Mount Kulal Biosphere taking measures. Finding a solution is also Reserve and the Tsavo National Parks particularly important for the vulnerable (Maundu et al., 2009). environment of coastal Kenya. The appearance of Prosopis juliflora in the area of Watamu (Kilifi county) threatens local 5 ecosystems. This particularly applies to the management to address the issue (Shackleton Kenyan coastal forest. More than 80 % of the et al., 2014). area is under some kind of protection (Matiku Using models, Shackleton et al. (2014) et al., unk.), and more than half of Kenya's assessed the management plans of countries rare plants are found in the coast region and found, that there is a link between action (WWF Kenya, unk.). Not only is the forest of and knowledge about the species. It was social and economic importance for the shown that the more information countries region, but it is also internationally recognized had about Prosopis juliflora, the better their for its unique and biologically rich ecosystems management was. From this, it is clear that and landscapes. Ecosystems on the coast vary increased knowledge on the plant and between rangelands, woodlands, terrestrial effective communication to the public is forests, mangroves, mudflats, coral reefs, essential to effective management. seagrass beds, estuaries, beaches, sand dunes, rivers, lakes, wetlands, cultural and natural There are various options of managing heritage sites. They provide natural resources invasive species, even leading to conflicts of for local communities, which are vital for interest regarding which one to use to supporting food security and subsistence preserve, exploit or enhance the plant’s activities in economic sectors like agriculture, benefits while reducing negative impacts. In fisheries, livestock, forestry, tourism, shipping, the end, the country’s socioeconomic status mining and energy. This significantly and the extent of the species’ spread play a contributes to production and socio-economic key role in determining which management is development at the local and national level as used (Shackleton et al., 2014). well as safety and well-being of coastal Management options include communities (WWF Kenya, unk.). An infestation of the coastal environment by (1) mechanical and chemical control, Prosopis juliflora is likely to deteriorate the (2) biological control ecosystems’ condition and compromise all (3) control through utilization benefits, and therefore must be prevented. (4) other control and (5) integrated management, which come along with different advantages 5. Possible solutions and disadvantages.

Over time, it seems that the costs of Prosopis Mechanical and chemical control juliflora – including the loss of livestock, expensive management and so on - exceed its This form of management is mostly used in benefits. When the invasion progresses, the wealthier countries and those with a minimal intraspecific competition increases and the spread of Prosopis juliflora. Mechanical plants produce less pods, which are the main control can be financially costly, which beneficial resource of Prosopis juliflora. became apparent in South Africa where a Instead, it forms dense thickets that make its partial removal of Prosopis juliflora costed use more difficult and cause negative impacts 2828 US Dollar per hectare (Shackleton et al., like the loss of grazing land, blocked 2014) infrastructures among others. Hence, many Therefore, it is important to use limited countries have implemented some form of financial (but also human) resources in the most effective way.

scale, but are also the most expensive In mechanical control, the plant can be killed controlling methods (Shackleton et al., 2014). by removing all of its roots to a depth of 30 Regarding chemical control with herbicides, cm, preventing it from sprouting again. This their potentially harmful effects on human can be achieved with different techniques and environmental health risks must not be from stick raking and grubbing to blade neglected. ploughing and chain pulling, the latter being the cheapest but also the least effective Biological control method. Chain pulling is recommended in combination with fire or chemical treatment Introducing a natural enemy of the invasive (Northern Territory Government, 2015). In species is a common way to deal with terms of costs and benefits blade ploughing is biological invasions. Both in Australia and the best option, which - according to the South Africa, these so-called biological control Australian Weed Management Guide on agents were released, although not very Mesquite (2003) - costs about 120 Australian successful in the latter. Dollar per hectare in dense infestations. In In Australia, however, two were able to such areas, a bulldozer can also be used as a establish widely (Shackleton et al., 2014). last resort (Northern Territory Government, Species of the genus Evippe, a leaf-tying moth 2015). from Argentina, have been able to severely Mechanical control prepares the soil for grass affect Prosopis populations. The introduction pastures, which can be assisted by sowing of the beetle Algarobius prosopis, which feeds grass seed. Since this also applies to the seeds on seeds, was also very successful, whereas it of Prosopis juliflora – which regenerates failed to establish in South Africa (Shackleton vigorously and has durable seeds - a follow up et al., 2014; Zachariades et al., 2011). Seed- control and monitoring is essential. feeding insects can regulate expansion of the (CRC for Australian Weed Management et al., plant but will not contribute to its removal. 2003). Instead, by thinning them, the insects prevent the formation of thickets, increasing future Australia also applies chemicals to combat usefulness. (Zachariades et al., 2011). different Prosopis species. One technique is To reach damaging densities the climate of the basal bark treatment, where an herbicide the area affected should meet the control is sprayed around the entire stem up to 7,5 agent’s demands. Also, possible predators of cm from the ground. Another method is the the species must be considered, as well as cut-stump technique. After cutting the tree other requirements. Hence, comprehensive horizontally, only leaving a stump very close to preparation is needed, which is often best the ground, the herbicide is applied within 15 determined through a model. This analysis seconds. helps estimating whether and where the For seedlings, it is recommended to spray species can be released and how it would foliar herbicide over the entire plant. These spread (van Klinken et al., 2003). The success plants should not be higher than 1,5 m and of Algarobius prosopis in Australia and the should have large area of foliage (CRC for failure of the same species in South Africa Australian Weed Management et al., 2003; reflect the importance of individually Northern Territory Government, 2015). assessing which species is suitable for which region. Both mechanical and chemical control are suitable to remove Prosopis juliflora at a large 7

Furthermore, a permit for the release of a While implementation costs are relatively low, biological control agent is required. initial research, on the other hand, is Precautionary measures are necessary due to expensive. In addition, in some areas control possible negative side effects on the agents have not yet had a substantial impact environment, such as attacks on non-target on density and spread. People that rely on species. One of the most popular examples is Prosopis juliflora for their livelihood are the introduction of the cane toad in Australia, nevertheless concerned (Shackleton et al., which was supposed to help with pest control 2014). but became a nuisance instead. In this case, there is concern that control Control through utilization agents might attack indigenous species of Prosopis such as Prosopis africana. On the A common argument against the control of other hand, Algarobius prosopis is already invasive Prosopis juliflora is its usefulness. spread in the range of the plant but has not Hence, combining management with been recorded from it (Zachariades et al., utilization can be a reasonable compromise. 2011). This method is especially useful in poorer Before releasing species like the very parts of the world, where expensive successful ones of Evippe, model analysis can management such as mechanical control is be made by institutions such as the IPM not feasible. Innovation Lab, which already helped to In Kenya, the government, the FAO and secure a permit to release the leaf-feeding several NGOs have taken time and effort to beetle Zygogramma bicolorata in Kenya and initiate programmes and build capacities to Uganda (Hendery, 2019). inform people about how to benefit from Prosopis juliflora (Shackleton et al., 2014). In addition to many small-scale projects, a cookbook was created to make use of the flour produced from the pods (Choge et al., 2007; Shackleton et al., 2014). Moreover, a thermal power station has recently been built in Baringo county where energy is produced by burning biomass of Prosopis juliflora (Herbling, 2016). Since regular pruning for charcoal production has proven to be a profitable way to take advantage of Prosopis juliflora while d. A beetle of the genus Algarobius controlling it at the same time (Wakie, Hoag, An advantage of biological control is the low et al., 2016), some argue that it should be costs, especially when compared to allowed for this species - bearing in mind the mechanical and chemical control. After the areas potential as another seed source. control agents are released, minimal Using Prosopis juliflora to generate income, associated costs are necessary as monitoring for instance by producing charcoal, can also is required. Another advantage over reduce overexploitation of indigenous species mechanical control is the possible application (Shackleton et al., 2014). of a control agent in large or inaccessible areas.

Control through utilization allows people to types that may have more thorns, bitter pods benefit from Prosopis juliflora and therefore and so on. promotes local development. In 2012, income Ultimately, the locational conditions from trading the products of Prosopis species determine on the actual potential for was estimated more than 1,5 million US Dollar utilization (Shackleton et al., 2014). in four selected areas. Despite the initial costs, for instance to inform people about different To avoid these problems and dangers of the options to use the plant, this form of utilization of Prosopis juliflora, indigenous management is considered to be cheaper than plants with comparable or better attributes the alternatives (Shackleton et al., 2014). for specific uses can be promoted and Instead of investing money, the control itself planted. For example, Acacia tortilis is becomes profitable. preferred by cattle to feed on the pods, plenty of other trees are also suitable for providing Despite some advantages, controlling Prosopis shade (Salvadora persica, Boscia angustifolia juliflora through utilization also has negative and Boscia coriacea) and Terminalia spinosa, impacts. for example, can be used for poles (Maundu First, the effectiveness depends on the desired et al., 2009). result, namely whether Prosopis juliflora should be completely eliminated or just prevented from spreading further. While Other control, integrated management and overall management needs many locals support the use and therefore the existence of Prosopis species, many others consider complete eradication as the best Other control solution (Shackleton et al., 2014). Other forms of control can also be used. One There also remains doubt about how much example is using fire to burn the plants, which the utilization of Prosopis juliflora actually is considered an inexpensive management contributes to its control, although it is method. evident that practices like flour production While fire might not harm Prosopis juliflora, destroy large amounts of seeds - since it is only known to cause severe damage approximately two million per tonne to Prosopis pallida, it can reduce its spread by (Shackleton et al., 2014). However, utilization removing vegetation and killing seeds on the could also lead to further distribution of seeds ground. and thus increase the spread (Wakie, Hoag, et Very intense fires could also kill other Prosopis al., 2016). species like Prosopis juliflora but do require

more preparation. Enough fuel must be Promoting the use of Prosopis juliflora can be provided, which can be achieved by using challenging, since it is often considered mechanical control such as chaining or inferior to native plants. reducing grazing before burning, and safety It also has the potential to push people into a measures must be taken so that non-targets business that creates a dependency, resulting stay untouched. The latter are also a reason in opposing attitudes towards Prosopis that fire cannot be used in all areas due to juliflora and conflicts of interest between increased risk of wildfires. stakeholders and the rest of the population. Ultimately, a permit should also be acquired Furthermore, plants differ from region to before this approach is attempted (CRC for region, leaving some people with less valuable

Australian Weed Management et al., 2003; Integrated management Shackleton et al., 2014). In 2014, almost half of the countries affected Another method is the so-called (partially) had an integrated management approach. girdling. A strip of the stem is removed before This includes three or more methods of those the growing season of the plant starts. It described above – biological control, should be at least 10 cm wide, reach deeply mechanical control, chemical control, control into the hard wood and go almost completely through utilization and other control around the tree. What remains is a vertical (Shackleton et al., 2014). This type of part of the stem (1/10 of the girth) that still management is often chosen by countries that allows the transport of nutrient reserves from have acquired a lot of knowledge about the roots to the crown. The weakening of the Prosopis juliflora, and it combines the tree leads to high nutrient consumption, and advantages (and disadvantages) of the various when the remaining strip of the stem is individual methods. In South Africa, removed - as well as the callus tissue and all mechanical, chemical and biological control is shoots from the stem - the assimilate used (Shackleton et al., 2014). Integrated transport is interrupted and photosynthesis management generally results in a better products cannot revert back to the root. The cost—benefit ratio and higher effectiveness in last strip is usually removed after the growing a long run (Northern Territory Government, season. It is recommended to repeat the 2015). procedure the next growing season(s), to kill the plant completely (Böcker & Dirk, unk.). Overall management needs Girdling has been applied in Europe to control the invasive Robinia pseudoacacia, which also Every form of management can be supported belongs to the family of by certain framework conditions. As Fabaceae/Leguminosae. mentioned before, knowledge determines The method inhibits massive sprouting after whether and which management is applied cutting back the tree, a common nature of and is vital to address invasive species both Prosopis juliflora and Robinia effectively (Shackleton et al., 2014). This is pseudoacacia. achieved, for example, with information about It is also a relatively inexpensive, efficient and the plant’s characteristics, where and how sustainable technique, in which the tree dies densely it has spread or could potentially automatically after some time (Böcker & Dirk, spread in the future (Clout & Williams, 2009). unk.). Knowledge is also essential to maximize the cost-benefit ratio and invest resources Nevertheless, girdling has never been optimally. implemented with Prosopis juliflora. The For example, it is possible to concentrate on species might react differently, also because areas where a further spread is most likely, or the environment is a different one. The best to take advantage of natural barriers results are achieved when the interventions preventing more spreading (Clout & Williams, are adapted to the beginning and the end of 2009). Areas with a high risk of further the growing season. spreading are, for example, water points Additionally, the method is difficult to where plants grow well and animals come to implement with small trees, multiple stems or drink (Northern Territory Government, 2015). thickets, because it takes some effort to apply Generally, it is better to intervene as early as to every tree (Böcker & Dirk, unk.). possible. 10

In an early stage, the infested area and its landowners, are informed about appropriate boundaries are less extensive, the success rate procedures. These could include working from is higher and the costs are lower (Clout & clean areas towards infested areas and make Williams, 2009). The management should be sure machines coming from infestations with aligned with the growth and reproductive Prosopis juliflora are clean. A national cycles of the species. Hence, control measures overview also helps to coordinate large-scale should be implemented before seed management, which is essential for the best formation (Northern Territory Government, possible result (Northern Territory 2015). Government, 2015; Shackleton et al., 2014). In Before taking action, it is also helpful to Kenya, there was a first meeting for a national prioritise an invasive species like Prosopis management strategy from 24th- 29th juliflora. Fighting on several fronts at the same November 2019, where the Kenya Forest time can be very ineffective and might bring Service, Kenya Wildlife Service, Ministry of no results at all (Clout & Williams, 2009). Agriculture and others gathered to discuss potential approaches (Eschen, 2020). If a plant has been successfully limited, management has not yet ended. Seeds or other sprouting parts can easily lead to Conclusion recurring infestations. Hence, follow up controls are necessary. In fact, successful Prosopis juliflora grows on 6 continents and management may take time and repetition to 129 countries but is only native to one see desired results (Northern Territory continent. By now, its invasive properties have Government, 2015). exceeded its benefits and are threatening Monitoring also provides feedback which can ecosystems and human health across the be used to modify, or, in case of a failed world. As a result, many countries are control, abandon the method of management implementing measures to control the plant’s (Clout & Williams, 2009; CRC for Australian spread. Weed Management et al., 2003)

The further spread of Prosopis juliflora should In Kenya, Prosopis juliflora has already caused be prevented. Sources of new infestations can severe damage and is now spreading further be areas with livestock or plantations. The in the coastal region of Kilifi county. The Australian Weed Management Plan for sensitive and unique coastal ecosystems are Mesquite (2015) recommends to quarantine threatened, necessitating urgent action. animals for at least eight days before The Convention on Biological Diversity (CBD) transporting them into uninfested areas. calls for a control or eradication of alien Moreover, grazing should be discouraged after species which threaten ecosystems, habitats control in order to promote the growth of and indigenous species, and is supported by grass and reduce new germination of Prosopis the declaration of the Kenyan government on juliflora (CRC for Australian Weed Prosopis juliflora, calling it a ‘noxious weed’. Management et al., 2003). Many countries have already started and Australia is also a model for developing a implemented forms of control and national management strategy and has management, which could serve as models for published several papers about control Kenya’s future approaches. measures. Through these resources, all parties affected, for example farmers and 11

It is still relatively inexpensive and easy to control Prosopis juliflora and implement management methods as it has not yet formed large-scale thickets or spread extensively and the success rate is still relatively high. Informing and involving local communities is also an essential element for the successful control and a satisfactory solution for everyone.

References

Literature

BioNET-EAFRINET. (o. J.). Factsheet—Prosopis juliflora (Prosopis or Mesquite). Abgerufen 8. Januar 2020, von https://keys.lucidcentral.org/keys/v3/eafrinet/weeds/key/weeds/Media/Html/Prosopis_juliflora_(Pr osopis_or_Mesquite).htm

Böcker, R., & Dirk, M. (unk.). Die neophytische Art Robinia pseudoacacia L. 16.

Chepkwony, C. C. and J. (2018, Juli 28). Mathenge tree, the weed from hell. The Standard. https://www.standardmedia.co.ke/article/2001289752/mathenge-tree-the-weed-from-hell

Choge, S., Pasiecznik, N., Harvey, M., Wright, J., Awan, S., & Harris, P. (2007). Prosopis pods as human food, with special reference to Kenya#. Water SA, 33(3), 6.

Clout, M. N., & Williams, P. A. (Hrsg.). (2009). Invasive species management: A handbook of principles and techniques. Oxford University Press.

CRC for Australian Weed Management, Commonwealth Department of the Environment and Heritage, Queensland Department of Natural Resources and Mines. (2003). Weed Management Guide—Mesquite (Prosopis species).

Damasceno, G. A. de B., Ferrari, M., & Giordani, R. B. (2017). Prosopis juliflora (SW) D.C., an invasive species at the Brazilian Caatinga: Phytochemical, pharmacological, toxicological and technological overview. Phytochemistry Reviews, 16(2), 309–331. https://doi.org/10.1007/s11101-016-9476-y

Damasceno, G. A. de B., Lopes Souto, A., Bezerra da Silva, I., de Araújo Roque, A., Ferrari, M., & Brandt Giordani, R. (2018). Prosopis juliflora: Phytochemical,Toxicological, and Allelochemicals. de Souza Nascimento, C. E., Tabarelli, M., da Silva, C. A. D., Leal, I. R., de Souza Tavares, W., Serrão, J. E., & Zanuncio, J. C. (2014). The introduced tree Prosopis juliflora is a serious threat to native species of the Brazilian Caatinga vegetation. Science of The Total Environment, 481, 108–113. https://doi.org/10.1016/j.scitotenv.2014.02.019

Ehrenfeld, J. G. (2010). Ecosystem Consequences of Biological Invasions. Annual Review of Ecology, Evolution, and Systematics, 4, 59–80.

El-Keblawy, A., & Al-Rawai, A. (2005). Effects of salinity, temperature and light on germination of invasive Prosopis juliflora (Sw.) D.C. Journal of Arid Environments, 61(4), 555–565. https://doi.org/10.1016/j.jaridenv.2004.10.007

Eschen, R. (2020). Developing a National Strategy for Prosopis juliflora in Kenya |. http://woodyweeds.org/?p=850

Hendery, S. (2019, Juli 12). IPM Innovation Lab Helps Uganda and Kenya Secure Permits to Fight Invasive Weed. https://www.agrilinks.org/post/ipm-innovation-lab-helps-uganda-and-kenya-secure- permits-fight-invasive-weed

Herbling, D. (2016). US firm Cummins starts 12MW Baringo power production in October. Business Daily. https://www.businessdailyafrica.com/corporate/US-firm-Cummins-starts-12MW-Baringo- power-production/539550-3356662-31m0dq/index.html

Matiku, P., Phil, M., & Box, P. O. (unk.). A national synthesis report for the development of the WWF- EARPO Eastern Africa Coastal Forests Ecoregion Programme. 43.

Maundu, P., Kibet, S., Morimoto, Y., Imbumi, M., & Adeka, R. (2009). Impact of Prosopis juliflora on Kenya’s semi-arid and arid ecosystems and local livelihoods. Biodiversity, 10(2–3), 33–50. https://doi.org/10.1080/14888386.2009.9712842

McNeely, J. (2001). Invasive species: A costly catastrophe for native biodiversity. 10.

Muller, G. C., Junnila, A., Traore, M. M., Traore, S. F., Doumbia, S., Sissoko, F., Dembele, S. M., Schlein, Y., Arheart, K. L., Revay, E. E., Kravchenko, V. D., Witt, A., & Beier, J. C. (2017). The invasive shrub Prosopis juliflora enhances the malaria parasite transmission capacity of Anopheles mosquitoes: A habitat manipulation experiment. Malaria Journal, 16. https://doi.org/10.1186/s12936-017-1878-9

Nawata, H. (2012). To Combat a Negative Heritage of Combating Desertification: Developing Comprehensive Measures to Control the Alien Invasive Species Mesquite (Propopis juliflora) in Sudan. Journal of Arid Land Studies, 4.

Northern Territory Government - Department Of Land Resource Management. (2015). Weed Management Plan for Mesquite(Prosopis spp.).

Proche, E., Wilson, J. R. U., Richardson, D. M., & Chown, S. L. (2008). Herbivores, but not other insects, are scarce on alien plants. Austral Ecology, 33(5), 691–700. https://doi.org/10.1111/j.1442- 9993.2008.01836.x

Shackleton, R. T., Le Maitre, D. C., Pasiecznik, N. M., & Richardson, D. M. (2014). Prosopis: A global assessment of the biogeography, benefits, impacts and management of one of the world’s worst woody invasive plant taxa. AoB PLANTS, 6. https://doi.org/10.1093/aobpla/plu027 van Klinken, R. D., Fichera, G., & Cordo, H. (2003). Targeting biological control across diverse landscapes: The release, establishment, and early success of two insects on mesquite (Prosopis spp.) insects in Australian rangelands. Biological Control, 26(1), 8–20. https://doi.org/10.1016/S1049- 9644(02)00107-X

Wakie, T. T., Hoag, D., Evangelista, P. H., Luizza, M., & Laituri, M. (2016). Is control through utilization a cost effective Prosopis juliflora management strategy? Journal of Environmental Management, 168, 74–86. https://doi.org/10.1016/j.jenvman.2015.11.054

Wakie, T. T., Laituri, M., & Evangelista, P. H. (2016). Assessing the distribution and impacts of Prosopis juliflora through participatory approaches. Applied Geography, 66, 132–143. https://doi.org/10.1016/j.apgeog.2015.11.017

WWF Kenya. (unk.). Coastal Kenya Programme | WWF Kenya. https://www.wwfkenya.org/coastal_kenya_programme_.cfm

Zachariades, C., Hoffmann, J. H., & Roberts, A. P. (2011). Biological Control of Mesquite ( Prosopis Species) (Fabaceae) in South Africa. African Entomology, 19(2), 402–415. https://doi.org/10.4001/003.019.0230

Pictures

a. Thorns of Prosopis juliflora; Forest & Kim Starr; Oahu, Keehi Lagoon, Hawaii, USA 2008. https://commons.wikimedia.org/wiki/File:Starr_080530-4655_Prosopis_juliflora.jpg

b. Flowers of Prosopis juliflora; J. M. Garg; Andhra Pradesh, India; 2009. https://en.wikipedia.org/wiki/Prosopis_juliflora#/media/File:Vilaiti_Keekar_(Prosopis_juliflor a)_W_IMG_6935.jpg

c. Thickets of Prosopis juliflora; J.M. Dufour-Dror https://www.researchgate.net/figure/Dense-thicket-of-Prosopis-juliflora-in-wadi-Ashan-in- the-Beer-Sheva-area-Israel-Photo_fig2_308071319

d. A beetle of the genus Algarobius; Robert Webster; Pryor, Oklahoma, USA; 2014. https://en.wikipedia.org/wiki/Algarobius#/media/File:Algarobius_P1090353a.jpg